Control mechanism



E. BREEJD CONTROL MECHANISM Filed Oct.

INVENTOR ENDEL BY @Mu 6;

ATTORNEY MAX Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE CONTROL MECHANISM Illinois Application October 5, 1932, Serial No. 636,282

6 Claims.

This invention relates to the control of motors and mechanisms actuated thereby, and among other objects aims to provide improved automatic means for limiting the operation of such motors or mechanisms.

The nature of the invention may be readily understood by reference to one illustrative construction embodying the invention and described in the following specification, certain pertinent features of such embodiment being illustrated in the accompanying drawing.

In said drawing:

Fig. l is a diagrammatic View of a limit switch controlling the electric circuits to motor driven apparatus;

Fig. 2 is an elevation of the limit switch in a neutral position;

Fig. 3 is a vertical section of the switch taken on the plane 3--3 of Fig. 4 showing the switch in an extreme position; and

Fig. 4 is a transverse vertical section of the switch taken on the plane 4-4 of Fig. 2.

The invention is here shown embodied in apparatus for stopping a motor and mechanism driven thereby when they reach a predetermined point and also for governing over-travel of the same beyond such point. Limiting apparatus of this character may advantageously be employed in many connections not only for the purpose of stopping mechanism at a predetermined point but to protect the mechanism against becoming jammed if it over-travel. Apparatus which has a reciprocating travel of varying amounts may advantageously be provided with the inventive 5 limitin apparatus to prevent accidental travel beyond a given limit. The illustrative apparatus is adapted not only to stop the motor when it reaches the limiting position but to reverse the same so as to be ready to travel in the opposite direction.

In many instances limiting and reversing mechanism may be applied at each end of the travel of the motor or the mechanism. For example, the illustrative mechanism may advantageously be employed in the weight recording mechanism of Brendel application, Serial No. 632,351, wherein a motor rotates a screw which causes a nut or the like to travel back and forth between certain limiting positions. If the motor be not stopped before the nut reaches one of the limiting positions, it is likely to jam and require disassembly before the apparatus can again be used. To control the effect of over-travel beyond the limiting position, the motor'is reversed and caused to travel in a reversed direction-for a short distance inside the extreme limits of travel and there brought to rest at a predetermined point. No jamming of the mechanism can thus result because of over-travel.

In Fig. l is diagrammatically illustrated an arrangement for controlling an electric motor (and of course the mechanism driven by it) The motor IE is a reversible motor, i. e. one having two separate field windings, one for counterclockwise rotation and the other for clockwise rotation. Such a motor has three terminals, one common terminal and the other terminals respectively for clockwise and counter-clockwise rotation. The motor is controlled by a reversing switch either manually or automatically 0perated which is herein represented by the movable switch member I l and spaced contacts l2 and IS with which the switch member may selectively be engaged. The contacts I2 and 13 are respectively connected to the terminals M and I5 respectively of the motor through a limit switch presently described. Contact l2 and terminal M in this instance control the motor for clockwise rotation and contact 13 and terminal I 5 control the same for counter-clockwise rotation. The movable switch member I I is connected to the common motor terminal it through the source of power supply. A line switch I! and fuse block ill are advantageously interposed in the line wires.

The limit switch I9 is provided with an oscillating switch throwing member 20 operated by the motor or apparatus driven by the motor. The actuating arrangement in this instance is a finger or earn 2! mounted on a shaft 22 which is geared relative to the motor or mechanism driven thereby to rotate substantially one revolution between the limiting positions of the apparatus. In other words, in traveling from one limit position to the other the finger 2| rotates once around the shaft. In one extreme position it engages the switch throwing member 29 on the right hand side (see Fig. 3). When moved to the other extreme position it rotates in a counter-clockwise direction and engages the left hand side of the member 28 (see dotted line position in Fig. 2). Any other appropriate mechanism may be provided for operating a switch throwing member at the extreme positions. In the present instance the finger 2| is connected to the motor or apparatus in a fixed relation so that it always moves in accordance with the operation of the apparatus and at no time is disconnected therefrom.

Where it is desired to arrest the motor at each of two extreme positions and reverse the same,

the limit switch is provided with similar or duplicate pairs of contacts for each of the limit positions. Contacts A, comprising a stationary contact element 23 and a movable contact element 24 are connected in series with the conductors 25 and 25 which lead from contact [2 to the clockwise rotation of terminal I4 of the motor. A companion set of contacts B, comprising contact elements 2? and 28 are similarly connected in series with contact l3 and terminal l5 through conductors 29 and 3E). The movable contact elements 24 and 28 are mounted so as to be separable from contacts 23 and 27 respectively, on flexible supports in the form of flat metallic leaf springs 3| and 32 whose ends are mounted on the body 33 of the limit switch and insulated from each other and the ground by appropriate insulating material (see Fig. 3) The wires 26 and 3%! are electrically connected to the anchored ends of the springs 3i and 32 respectively.

When the motor or mechanism reaches its extreme position on counter-clockwise rotation for example, finger 21 engages the member 20 and moves it to the left (see Fig. 3) until contacts 21 and 28 are separated, thus breaking the circuit through the motor. When the motor reaches its extreme position on clockwise rotation, finger 2i engages the opposite side of member 23 and moves it to the right until it separates the contacts A thus breaking the circuit for clockwise rotation.

During the first of the aforesaid operations, it should be noted however that when the motor is rotating in a counterclockwise direction the switch element H is in contact with the contact 13. Thus, although the contacts A are closed when the contacts B are open, nevertheless no circuit can be established through the contacts A for clockwise rotation since the controlling switch element is not in contact with the contact 12. Similarly when the limit of clockwise rotation is reached and the contacts A are open, no circuit may be established through contacts B even though they are closed since the controlling switch is not closed on contact l3.

Since in most instances a motor will coast beyond its limit position even though the motor circuit is open, the limit switch in this instance is advantageously provided with means for controlling the motor in the event of such over-travel.

Such control is important since successive overtravel might cause the mechanism to jam or break. In the present instance pairs of reversing contacts C and D are provided for reversing the motor shortly after the contacts A or B respectively are opened. Similar pairs of contacts C and D are provided in the present case since it is desired to reverse the motor at each of the extreme positions in the event of over-travel. The contacts C and D comprise movable contacts 34 and 35 adapted to engage a stationary contact, in this case a common contact 36, which extends across the body of the switch and is connected through wire 37 with the wire leading from switch element i! to the common terminal l6 of the motor (through the line switch and fuse block as previously noted). The movable contacts 34 and 35 are respectively mounted on movable supports in the form of flat springs 38 and 39 which are connected to the wires 26 and 39 respectively leading to the clockwise and counter-clockwise terminals of the motor respectively. The contacts C and D are arranged to be closed respectively shortly after the opening of contacts B and A respectively. This sequence of operations is advantageously efiected in the present instance 105 mounting the leaf springs 38 and 39 inside the leaf springs 3i and 32 respectively and holding them out of contact with the common contact member 36 by a floating separator d9 made of insulating material and passing through and held in an opening of the body of the switch. The length of the separator 49 is adjusted so as to permit the contacts D to close shortly after the contacts A have opened and to permit the contacts C to close shortly after the contacts B have been opened (see Fig. 3). It should be noted that the leaf springs 38 and 39 are perforated at il at a point in register with contacts 24 and 28 respectively to allow the latter to pass freely through the same. The interval between the opening of contacts B and the closing of contacts C may be of course varied by varying the length of the separator All. This interval represents the period during which the motor may freely over-travel. It should of course not be so great as to allow a dangerous amount ofover-travel such as might result in a jam and yet it should not be so short as to result in too prompt a reversal of the motor (as presently described) since that would cause an excessive amount of hunting until the motor was brought to rest. Nevertheless if it be necessary to work between close limits the switch may be adjusted to secure a very prompt reversal of the motor if it coast beyond the limit position.

As indicated above if the motor over-travels sufiiciently after opening contacts B or A (as the case may be) to close contacts C or D, an immediate reversal of the motor will take place. For example, if switch i i be closed on contact 3 for counter-clockwise rotation, the closing of contacts C (after the limit of counter-clockwise rotation has been reached and the contacts B opened) will establish a circuit through the line and wire 3! with the clockwise terminal I4 and immediately reverse the motor. Such reversal will cause the cam 2! to travel toward the right (see Fig. 3) until it openscontacts C. If upon opening of the contacts 0 the motor travels too far and allows contacts 13 to close, it is then again reversed and the operation repeated thus causing the motor to hunt a specific stopping point wherein contacts B and C are both open. When the control switch H is closed on contact 2 for clockwise rotation, the motor when reaching its limit of travel will be successively reversed (assuming it over-travels) until it hunts a specific position wherein both contacts A and D are open. In each of the above instances however, the motor is ready to travel in the opposite direction away from its limit position when the switch is closed on the contact.

It is apparent from the foregoing that limits may be adjusted to permit safe operation very close to the absolute limits of possible travel without causing breakage or a jam notwithstanding the tendency of the motor or apparatus to overtravel. The adjustment may be such to cause a very prompt reversal of the motor upon any substantial over-travel. It should be noted that the switch H and its contacts l2 and 13 may either be manually operated or automatically operated as desired. In the specific application to the weight indicating mechanism above mentioned, the switch member H is operated by the scale beam to cause the motor to travel in response to the movements of the scale beam. Nevertheless, the motor and associated mechanism are protectedagainst damage in the event the scale beam moves to extreme positions.

Obviously the invention is not limited to the details of the illustrative construction since these may be variously modified. Moreover it is not indispensable that all features of the invention be used conjointly since various features may be used to advantage in diiferent combinations and sub-combinations.

Having described my invention, I claim:

1. Control means of the character described comprising in combination a driving motor, a limit member to be moved by the motor on approaching limit position, a reversing switch controlled by said limit member and adapted to reverse said motor and cause the same to return a distance inside its extreme position, said reversing switch having a contact which is opened when the motor returns a short distance to stop said motor, and a pair of contacts operated by said limit member which are left closed when the motor comes to rest to maintain a circuit adapted to actuate the motor in the opposite direction only when power is applied to the motor.

2. Controlling apparatus of the character described comprising in combination a reversible motor, a limit switch operated by said motor, said switch having a pair of opposite moving contacts adapted to be alternately moved by the motor on reaching its respective extreme positions, another pair of opposite contacts normally held open and adapted to close alternately after the opening of the first named contacts, said first named contacts being connected to open the motor circuit, and said last named contacts being arranged to reverse the motor.

3. Controlling apparatus of the character described comprising in combination a reversible motor, a limit switch having a body of insulating material carrying a pair of opposite contacts resiliently mounted on said body and electrically connected with the respective motor operating circuits, a cam member operated by said motor and lying between the contact mountings to open the contacts respectively on reaching predetermined positions, and another pair of resiliently mounted contacts, a separator for normally holding said contacts open, said other pair of contacts being operated by said cam to close respectively after the corresponding first named contact has been opened and being connected to reverse the motor.

4. Controlling apparatus of the character described comprising in combination a reversible motor, a controlling switch carrying a pair of opposing contacts mounted on leaf springs and adapted to close respectively on stationary contacts carried on the switch body, a rocking member on the switch body adapted to open said contacts alternately, said contacts being connected with the motor to rotate the same in a clockwise and counter-clockwise direction respectively, a cam operated by said motor on reaching its respective limit positions to engage said rocking member and open the corresponding contacts to stop the motor, a stationary switch point, a pair of movable switch points normally adapted to close on said stationary switch point but held open and operated by said cam to close on said stationary points alternately if said motor substantially overruns its limit position, said switch points being connected with said motor to reverse the same when respectively closed.

5. Controlling apparatus of the character described comprising in combination a reversible motor, a controlling switch carrying a pair of opposing contacts mounted on leaf springs and adapted to close respectively on stationary contacts carried on the switch body, a rocking member on the switch body adapted to open said contacts alternately, said contacts being connected with the motor to rotate the same in a clockwise and counter-clockwise direction respectively, a cam operated by said motor on reaching its respective limit positions to engage said rocking member and open the corresponding contacts to stop the. motor, a stationary switch point, a pair of movable switch points carried on flat springs inside the respective movable contacts and controlled by said rocking member to close respectively after opening a contact point when the motor substantially overruns its limit position, said points being connected with said motor to reverse the same, and a separator for normally holding said points open and permitting only one at a time to close on the stationary switch point.

6. Controlling apparatus of the character described comprising in combination a reversible motor, a motor control reversing switch for respectively controlling the operation of the motor in difierent directions of rotation, said reversing switch having a pair of spaced contacts and a controlling contact adapted selectively to engage said spaced contacts to control the direction of rotation of said motor, said spaced contacts being spaced sufficiently to prevent simultaneous engagement of both by said controlling contact and to provide an intermediate position where the controlling contact does not engage either of said spaced contacts, a lim t switch operated by said motor and connected with said controlling switch contacts to open the circuit through the active controlling switch contact and close a circuit through the other contact to reverse the motor when the control switch is reversed, said limit switch having a pair of terminals opened by said motor on reaching a predetermined limiting position, and a pair of terminals closed by a small predetermined over-travel of said motor beyond said limiting position, and means for closing said latter terminals promptly but only after the first pair of terminals is opened, said latter terminals being connected to reverse said motor to return it to said position.

MAX E. BRENDEL. 

